Abstract: Mild Cognitive Impairment (MCI) carries a high risk of progression to dementia due to Alzheimer's disease (AD). Yet, there are currently no effective treatments. For older adults with MCI, the cognitive problems and uncertainty they face negatively impacts their everyday functioning, capacity and confidence to engage in challenging cognitive activities, and thus their quality of life. A substantial proportion of adults with MCI either take cholinesterase inhibitors or have tried them, but the low efficacy of these approved treatments for AD appears outweighed by their side effects. The goal of this study is to test the efficacy of a non-pharmacological treatment for MCI that involves noninvasive brain stimulation (NIBS). Early studies in AD dementia patients have found that repetitive transcranial magnetic stimulation (rTMS, a form of NIBS) improved global cognitive function and activities of daily living. Given that in AD, neuronal loss and synaptic dysfunction progress along brain networks, these early studies of brain stimulation in AD dementia suggest there is sufficient neuroplasticity for efficacious effects of brain stimulation. Of the very few rTMS studies in MCI that have been published, the effect size appears to be moderately large. However, it is not clear whether the dorsolateral prefrontal cortex (DLPFC), the stimulation site used in most of the prior MCI/AD rTMS trials, is the optimal site for achieving the most efficacious effects including effects on episodic memory. Importantly, when other investigators used rTMS to stimulate a lateral parietal cortical (LPC) site in healthy young adults, significant effects of rTMS on memory were measurable weeks later. Moreover, functional connectivity of brain regions was selectively increased, including the posterior cingulate cortex (PCC), a ?hub? of brain networks that is affected in amnestic MCI. Because stimulation of the DLPFC and the LPC may each have distinct effects, we designed this pilot trial to have two active rTMS treatment groups: DLPFC and LPC. A third group, a sham-control, will also be included to achieve a controlled, randomized, double-blind trial. For each of the three groups, stimulation will be bilateral, based on effects achieved in the AD studies. The primary hypothesis is that active rTMS (to either site of stimulation) will be superior to sham-control in improving memory. Measures of change in functional connectivity will be computed to examine whether there is evidence that rTMS changes connectivity of the PCC with other regions of the brain. In addition to looking at effects of rTMS on functional connectivity and cognition in relation to the cortical site stimulated, genetic markers will be collected toward addressing heterogeneity of response. To track the durability of rTMS effects on memory, participants will be followed longer than in any prior study (up to 6 months after the intervention). If this study finds rTMS improves memory in older adults with MCI, further clinical development of this non-pharmacological treatment could ultimately improve the lives of millions of older adults who have MCI and are at an increased risk of developing dementia.